首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   62373篇
  免费   4895篇
  国内免费   2844篇
电工技术   3306篇
技术理论   6篇
综合类   4166篇
化学工业   10493篇
金属工艺   3872篇
机械仪表   3835篇
建筑科学   4696篇
矿业工程   2298篇
能源动力   1963篇
轻工业   3495篇
水利工程   1090篇
石油天然气   4634篇
武器工业   460篇
无线电   6510篇
一般工业技术   7266篇
冶金工业   3373篇
原子能技术   729篇
自动化技术   7920篇
  2024年   249篇
  2023年   997篇
  2022年   1723篇
  2021年   2465篇
  2020年   1865篇
  2019年   1690篇
  2018年   1877篇
  2017年   2069篇
  2016年   1896篇
  2015年   2405篇
  2014年   3134篇
  2013年   3563篇
  2012年   3683篇
  2011年   4012篇
  2010年   3711篇
  2009年   3304篇
  2008年   3284篇
  2007年   3217篇
  2006年   3196篇
  2005年   2770篇
  2004年   2048篇
  2003年   2164篇
  2002年   2485篇
  2001年   2082篇
  2000年   1614篇
  1999年   1714篇
  1998年   1257篇
  1997年   1071篇
  1996年   1107篇
  1995年   847篇
  1994年   634篇
  1993年   472篇
  1992年   366篇
  1991年   275篇
  1990年   208篇
  1989年   171篇
  1988年   153篇
  1987年   89篇
  1986年   70篇
  1985年   38篇
  1984年   38篇
  1983年   27篇
  1982年   25篇
  1981年   15篇
  1980年   22篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1974年   1篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
提出了以对二氯苯为原料,经硝化,水解和还原三步合成2-氨基-4-氯苯酚的讨了影响反应的因素。产品总收率达77%。  相似文献   
172.
The paper is the second in the series of two analyzing the h-p version of the finite element method. It generalizes the results of the first part (Guo, Babuska 1986) and presents computational results.Supported by the NSF Grant DMS-8315216Partially supported by ONR Contract N00014-85-K-0169  相似文献   
173.
一种新型的激光—等离子体辅助化学气相沉积装置的研究   总被引:1,自引:0,他引:1  
为探索用激光离子体共同辅助化学气相沉积过程以实现室温沉积的可能性,设计并制造了一种新型的CVD装置,实际了SiH4-NH3-N2体系制取Si3N4膜的试验。结果表明,激光和等离子体是可以相互促进,共同辅助CVD过程的,且两者均处于较代的能量水平。  相似文献   
174.
175.
Solid-state emissive organic materials have received increasing attention due to their prospective applications in large-area. Here, a novel π-extended tetrathiafulvene derivative DPD with donor-π-donor structure has been newly developed to produce the prominent characteristic of aggregation-induced enhanced emission (AIEE) that exhibits higher fluorescence quantum efficiency in solid film compare to its solutions. The AIEE mechanism of DPD was studied in detail through photophysical investigations and can be dominant attributed to the formed excimer state of DPD and J-aggregates in solid state.  相似文献   
176.
In this study,the nitrogen removal performance of partial denitrificaiton/anammox(PDA) process was investigated by using an UASB reactor.High total nitrogen(TN) removal efficiency(91.97%) was achieved at an influent nitrogen loading rate of 0.64 kg/(m3·d).Anammox bacteria did execute the function of converting nitrate to nitrite in PDA system according to 15N isotope labeling experiments and the contribution was approximately 36.3%.Candidatus_Brocadia,Candidatus_Kuenenia an...  相似文献   
177.
郭振建 《灯与照明》2022,46(1):24-26
道路照明灯具的布置方式与灯具的安装高度、间距等密不可分,采用双侧交错灯具布置方式应满足《城市道路照明设计标准》(CJJ 45—2015)的相关要求。为使相关照明值达到规范标准,分析此种布置方式的设计要求。  相似文献   
178.
Low pH-induced alterations in gene expression profiles and organic acids (OA) and free amino acid (FAA) abundances were investigated in sweet orange [Citrus sinensis (L.) Osbeck cv. Xuegan] leaves. We identified 503 downregulated and 349 upregulated genes in low pH-treated leaves. Further analysis indicated that low pH impaired light reaction and carbon fixation in photosynthetic organisms, thereby lowering photosynthesis in leaves. Low pH reduced carbon and carbohydrate metabolisms, OA biosynthesis and ATP production in leaves. Low pH downregulated the biosynthesis of nitrogen compounds, proteins, and FAAs in leaves, which might be conducive to maintaining energy homeostasis during ATP deprivation. Low pH-treated leaves displayed some adaptive responses to phosphate starvation, including phosphate recycling, lipid remodeling, and phosphate transport, thus enhancing leaf acid-tolerance. Low pH upregulated the expression of some reactive oxygen species (ROS) and aldehyde detoxifying enzyme (peroxidase and superoxidase) genes and the concentrations of some antioxidants (L-tryptophan, L-proline, nicotinic acid, pantothenic acid, and pyroglutamic acid), but it impaired the pentose phosphate pathway and VE and secondary metabolite biosynthesis and downregulated the expression of some ROS and aldehyde detoxifying enzyme (ascorbate peroxidase, aldo-keto reductase, and 2-alkenal reductase) genes and the concentrations of some antioxidants (pyridoxine and γ-aminobutyric acid), thus disturbing the balance between production and detoxification of ROS and aldehydes and causing oxidative damage to leaves.  相似文献   
179.
The method of implicit curve-fitting and explicit-calculation has been used for fast and stable calculations of thermodynamic properties of subcritical refrigerants. In order to extend that method to the critical pressure, a method of sectional implicit curve-fitting and explicit-calculation for refrigerant thermodynamic properties is introduced in this paper. The whole data range is divided into several subsections. The requirements on the continuity of thermodynamic properties and the first order derivative of thermodynamic properties in the intersection points of subsections are indicated, and the methods to meet the requirements are presented. Quadric equations are constructed instead of curve-fitting when no data can be given. With the source data obtained from REFPROP 7.1, explicit fast calculation formulae for thermodynamic properties of R410A, covering the saturated temperature of 213.15–344.51 K and superheat of 0–65 K, are given as an example. The calculation speeds of the formulae of R410A are more than 7000 times faster than those of REFPROP 7.1 while the total mean relative deviation of the fast calculation formulae from REFPROP 7.1 is only 0.04%.  相似文献   
180.
我们三胶行业属于资源综合利用行业,用牲骨通过一系列加工制得明胶、骨胶、磷酸氢钙、骨粉、骨油等产品。但在生产过程中耗用大量的水、盐酸、石灰等,也产生了大量的废水,且较难治理。在全社会日益重视环境质量的情况下,我们行业的企业应下力气按照“循环经济”的发展模式,努力  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号